A CORROSION  COMPARISON  OF  SEV- 
ERAL METALS  USED  AS  CATHODES 
IN  ELECTROANALYSIS 


BY 


KDWIN  HERBERT  WEBSTER 


THESIS 

FOR  THE 


DEGREE  OP'  BACHELOR  OP'  SCIENCE 

IN 

CHEMICAL  ENGINEERING 


COLLEGE  OE  LIBERAL  ARTS  AND  SCIENCES 

UNIVERSITY  OF  ILLINOIS 


1922 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/corrosioncompariOOwebs 


1322 

\Y39 


UNIVERSITY  OF  ILLINOIS 


i922.__ 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 

.Eilwiii  _ KeiLuBX  t_  ex 

ENTITLED A-0-Q.rxQ£lia2i-JlQiipxD:i  F.  on  -nf.  J5£-xex£JL-Y-ntiilp- 

-JIl££.C— a.s-CAtl-Qjlea--iji-ni£ij.txQa.nal^sx£^ 

IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF 3acLelQr._jaf_^ci-enae.__jLii-_CLeiLlcLLL_Xii^ijiBj£ij:'j_ag 


HEAD  OF  DEPARTMENT  OF CLemisiry. 


TABLE  OY  COIfTEBTS 


page 

I.  IITTPOPIJOTIOU  1 

II.  EISTOEICAL  2 

III.  EZPEBE^ITTAL  4 


1. 

Material 

4 

2. 

Procedure  and  Piagrem 

9 

IV. 

EESULTS 

11 

1. 

Silver  Eitrate  Solutions 

11 

2. 

CJoLalt  Sulphate  Solutions 

11 

3. 

Colalt  Eitrate  Solutions 

11 

4. 

Eiekel  sulphate  Solutions 

11 

5. 

Eickel  Eitrate  Solutions 

12 

6 • 

Oopper  sulphate  Solutions 

12 

7. 

Copper  Eitrate  Solutions 

12 

8. 

Zinc  Acetate  solutions 

12 

V. 

PI 

SCUSSIOE 

14 

VI. 

Sm2I/.EY 

19 

VII. 

BIBLIOaBAPEY 

20 

"i»  , ' 'MV, 
,1  ,■  ' ■• , y 1 ii  f ’ 

' '-.s^ 

’*  ^ »i.* ' 


AOMOV/IEDGMIEITT 

I v;ish  to  express  my  appreoi&tion  to  It.  G-.I.  Be&l 
and  to  tliank  Mm  sincerely  for  the  many  suggestions  and 
aids  given  during'  the  preparation  of  this  thesis. 


PART  I 


IHTEOPUCTIOH 

Tliere  is  little  materir.1  available  in  the  literature  from 
from  which  a suitable  comparison  of  the  various  metals  ordinarily 
used  for  cathodes  in  electroanalysie  may  be  drawn.  The  few 
studies  that  havie  been  made  are  referred  to  in  the  bibliography 
and  discussion;  however,  it  was  desired  to  learn  something  of  the 
behavior  of  these  metals  when  a series  of  quantitative  electro- 
analyses were  performed  under  identical  conditions. 

This  was  done  by  studj^-ing  the  successive  losses  by  corrosion 
of  a set  of  cathodes  of  the  various  metals  used  in  precipitating 
the  five  metals  commonly  determined  in  the  elementary  state . 

Prom  the  data  obtained  it  is  to  be  noted  that  there  is, in  general, 
a superiority  of  one  metql  over  another  for  the  purpose. 


PART  II 
HISTORICAL 

Rroffi  the  empirical  state  of  affairs  common  to  ever^'  neYJ 
■branch  of  science  the  chemistry  of  electroanalysis  has  "by  reason 
of  prolific  investigation  become  fairly  definite  and  well  organiz- 
ed. However , there  are  phases  in  its  application  that  are  as 

yet  undeveloped  and  insufficiently  investigated. 

Hollowing  the  discovery  by  Uicholsen  and  Carlisle  in  1800 
of  the  decomposition  of  water  by  the  electric  current,  Cruik- 
shank  observed  the  separation  of  metallic  copper,  and  suggested 
the  galvanic  current  as  a qualitative  agent  for  the  determination 
of  the  metals. 

The  discovery  of  galvsnoplasty , known  as  electropit ting, 
a technical  process  closely  allied  to  electroanalysis , dates  from 
1859,  as  made  by  Jacobi. 

Since  then  many  investigators,  prominent  and  unknown,  have 

1 

observed  the  electroljT-tic  behavior  of  solutions  of  the  s^lts  of 
the  various  metals  from  the  standpoint  of  the  chemistry  of  the 
deposited  metal.  At  first  qualitative,  then  quantitative,  the 
work  has  been  extended  to  all  classes  of  solutions,  and  to  in- 
clude many  of  the  known  metals,  and  also  a few  of  the  nonmetallic 
elements . 

Attention  of  investigators  has  been  largely  dravm  to  the 
chemical  reactions  of  the  electrolytic  cell,  the  metals  suited 
to  electrolytic  deposition,  the  best  solutions,  and  the  proper 


-3- 

su'Dstances  to  "be  adde^  to  tlrjese  solutiozis,  whereas  the  source  of 
the  current,  the  physical  conditions  of  the  experiment,  and  the 
electrode  mFiterials  have  not  been  fully  investigated,  the  last 
only  c casually  hy  investigators  in  related  fields. 

For  a period,  now  on  the  wane,  it  was  "believed  that  all 
elements  could  "be  determined  electrolytically ; this  belief  natur- 
ally stimulated  research  on  nearly  all  the  known  metals,  and 
nonmetals.  In  the  coursemof  this  there  were  investigated  and  de- 
veloped, the  current  sources,  the  vessels,  the  stirring  devices, 
and  simultaneous  operation  on  many  samples,  however,  there  has 
been  practically  no  work  specifically  on  corrosion  of  electrodes 
by  the  electrolytes  used  in  common  electroanalytic  practice. 

The  Division  of  Analytical  Chemistry  of  the  University  of 
Illinois  has  been  desirous  of  obtaining  some  criteria  of  the 
metals  in  common  electrode  use  as  to  their  resistance  to  corrosion 
in  solutions  of  salts  of  the  metals  commonly  determined  electro- 
lytically. There  has  been  no  previous  work  done  along  this  line 
at  the  University  of  Illinois;  this  problem  was  taken  up  in  19E0 
at  the  suggestion  of  Dr.  G.D.  Beal  with  a view  to  obtaining  in- 
formations along  this  line. 


-4- 

PABT  III 
FXPPHBTITTAL 
1.  Materiel 

In  the  successful  completion  of  an  investigation  such  as 
this  it  is  necessary  to  use  metals  whose  salts  m.ay  "be  obtained 
in  forms  which  are  easily  and  accurately  determined,  and  of  such 
a nature  that  comparable  results  may  be  obtained.  To  this  end 
chemically  pure  silver  nitrate,  copper  sulphate,  copper  nitrate, 
cobalt,  sulphate,  cobalt  nitrate,  nickel  sulphate,  nickel  nitrate, 
and  zinc  acetate  were  Tised.  The  silver  nitrate  was  99. 98^-  pure 
as  tested  by  the  average  of  three  electrolytic  determinations. 

Both  the  copper  nitrate  and  sulphate  contained  iron,  approximately 
0.08f^',  v''hich  was  removed  from  them  by  ammonia  precipitistion  of 
each  sample,  giving  a solution  containing  in  addition  tb  the  cop- 
per salt,  armnonium  nitrate  and  sulphate,  respectively.  Similarly 
each  solution  of  cobalt  and  nickel  was  freed  from  iron,  for  though 
iron  does  not  interfere  seriously  with  electrolysis  of  ammoniacal 
solutions,  it  is  bothersome,  and  may  cause  results  to  include 
some  mechanical  error.  All  chemicals  used  were  of  either  the 
J.T.  Baker  or  Baker  8 Adamson  make. 

The  concentration  of  all  solutions  used  for  the  deposi- 
tion was  ascertained  b^/  strictly  chemical  as  well  as  electrolytic 
methods,  and  the  results  compare  very  satisfactoril37.  The  con- 
centration of  stock  solutions  was  a variable,  0.003  to  0.005  g/cc 
of  metal  being  the  rule,  save  for  the  copper  and  Kinc  solutions; 
the  concentration  of  the  copper  solutions  was  appror.imetely  0.003 
g/cc,  and  that  of  zinc  0.015  g/oc,  expressed  for  the  metals* 


A description  of  the  standardization  of  these  solutions  follows: 
Silver  filtrate 


25cc  portions  were  analyzed  graviwetricf'lly  hy  pre- 
cipitation as  silver  crloride;  the  five  determinations  gave  results 
of  0.1571,  0.1578,  0.1580,  0.1578,  end  0.1677  grams  of  ^gCl  respec- 
tively. The  average  of  these  corresponds  to  a concentration  of 
0.11876  g/25  cc  of  0.00475  g/cc  of  silver'. 

Copper  Sulphate 

25  cc  portions  were  analyzed  hy  the  low  iodometric 
method  as  described  by  Treadwell-Hall^  for  sodium  thiosulphate 
standardization;  the  sodium  thiosulphate  was  strndardized  against 
C.P.  copper.  Four  of  these  portions  required, respectively , 1£.78, 
12.78,  12.78,  find  12,80  cc  of  a solution  of  sodium  thiosulphate 
having  a copper  equivalent  of  C. 006249  g/cc.  This  gives  the 
value  of  the  copper  sulphate  solution  as  0.0021975  g/cc  of  copper. 

Copper  titrate 

Similar  determination  of  copper  in  this  solution 
gave  the  concentration  as  0.0041156  g/cc  of  copper. 

I?ickel  Sulphate 

determination  of  the  nickel  as  nickelodimethyl- 
glyoxime  in  20cc  samples  gave  weights  of  the  glyozime , amounting 
respectively , to  0.2910,  0.2912,  0.2909,  0.2913,  and  0.2911  from 
the  average  of  which  the  concentration  of  the  solution  was  deter-.- 
mined  to  be  0.002965  g/cc  of  nickel. 

ITickel  litrate 


Similar  analyses  of  i 


i 


( 


V 


\ 


‘i 


i 


LI 


-6- 


average  value  of  concentration  as  0*0029146  g/cc  of  nickel. 

Cobalt  Sulphate 

The  cohaltie  hydroxide  wae  precipitated  hy  sodium 
hydroxide  and  bromine,  was  ignited,  and  reduced  by  hydrogen,  in 
8 Eose  crucible,  to  metallic  cobalt.  this  method  26  cc  sam- 
ples of  the  stock  solution  gave  0.1476,  C.1475,  0.1476,  0.1474, 
and  0.1476  grams  of  metallic  coba.lt,  corresponding  to  a solution 
concentration  of  0*005900  g/oc  of  cobalt. 

Cobalt  nitrate 

Similar  treatment  of  25cc  samples  of  this  solu  - 
tion  gave  an  average  value  of  0*1372  grams  of  cobalt,  correspond- 
ing to  a concentration  of  0.C05486  g/ce  of  cobalt. 

"ine  Acetate 

The  zinc  solution  was  analyzed  by  precipitation  of 
zinc  carbonate,  and  careful  ignition  of  this  to  the  oxide.  Five 
determinations  gave  0.1862,  0*1863,  0.1867,  0.1861,  and  0.1864  ‘ 

grams  of  the  oxide,  respectively,  corresponding  to  a concentra- 
tion of  0.006989  g/ce  of  zinc. 

by  electrolytic  analysis  the  following  results  ?/ere  obtained; 
Silver  titrate 

26  cc  portions,  electrolyzed  according  to  a method 
£,iven  in  Classen-Eall  gave  a concentration  of  silver  of  0.004749 
g/ce  of  silver,  an  average  of  four  close  checks. 


II 


■1 


a 


i 


-7- 


Oopper  Sulphate 

S5  oc  portions,  when  electrolyzed,  eccording  to  s 
method  given  in  Classen-Hsll^®’  gave  0.00320  g/co  as  the  concen- 
tration in  terms  of  copper. 

Copper  ITitrste 

25  cc  portions,  to  which  v/ere  added  2cc  of  SIT  H^SO^ 
and  2 drops  of  SU  ECl,were  filtered  free  from  contaminating  AgCl, 
and  diluted  to  approximately  75  cc;  to  each  was  added  5 cc  of  con- 
centrated E2T0g  and  one  gram  of  urea.  They  were  electrolyzed  at 
0. 7-0.8  amperes  and  3o0.3.5  volts  for  80  minutes.  The  deposit  of 
metal  was  dried  oy  an  alcohol  wash,  followed  oy  the  burning  off 
of  the  alcohol.  This  is  the  method  as  used  by  the  Division  of 
Analytical  Chemistry  of  the  University  of  Illinois,  and  the  con- 
centration found  was  0.00410  g/cc  of  copper. 

Uickel  Sulphate . 

This  solution,  analyzed  according  to  the  method 
given  by  Classen-Hall^ , modified  fi>r  the  presence  of  nitrates, 
shov/ed  a concentration  of  0.002911  g/cc  of  nickel. 

Cobalt  Sulphate 

The  method  for  the  determination  of  cohalt  paralle 
that  for  nickel,  and  the  same  method  was  used  as  for  nickel.  The 
concentration  found  v/as  0.005904  g/cc  of  cobalt. 

Cobalt  nitrate 

A concentration  of  0.005478  g/cc  of  cobalt  was  ob- 
tained by  a method  identictll  with  that  described  for  the  nickel 


nitrate 


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-8- 


Zino  Acetate 

The  analysis  ¥/as  carried  out  according  to  Olassen- 
Eall^in  acetic  acid  solution.  1 cc  =*  0o00597  g/cc  of  zinc. 

A comparative  chart  of  the  chemical  and  electrolytic 

standardizations  of  the  salts  employed,  e:^pressed  in  grams  of  the 

metal  per  cc  of  the  solution  follows: 

AgEO^  CuSO/  Cuno.,:  EiSO/  EiEOr. 

Chemical  0.C04750  0.0031955  0.0041136  0.00E965  0.00E9I45 

Electrolytic  0o004749  0.00320  0.00410  0.002960  0.002911 

O0SO4  C0EO5  ^nfCgEsO^)^ 

Chemical  0.0059  0.005488  0.005989 

Electrolytic  0*005904  0.005478  0.005970 

The  values  obtained  by  electrolytic  analysis  have 
been  assumed  as  correct,  because  they  are  subject  to  exactly  the 
same  errors  as  occur  later  in  the  corrosion  tests,  compensating 
these.  This  work  was  all  done  on  a special  electrolysis  setup, 
diagrammed  on  the  following  sheet,  with  stationary  platinum 
cathodes  of  gauze,  and  rotating  wire  spiral  anodes,  in  2oocc  flat 
bottomed  EonSol  beakers. 


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-9- 


DIAGRAi:  OF  TEE  EIEGTEIGAL  GOIETECTIOES  FOR  TEE  TE^T 
ELEGTROLYSES.  CATEOEES  STATIOEAEY'i  AEOEES  ROTATING. 


A. 



A 

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TIORARY 

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ELEGTROLY 

SES  IS  EE/iGTLY  SPAILAR. 

LEGERD:  A Ammeter 

Tf  Voltmeter 

RHIAPJCS:  An  £.mmeter  for  encE  circuit,  and  one 

voltmeter  connected  with  all  or  any  of  the  five  circuits,  was 
the  scheme  used  for  as  near?uy  uniform  conditions  of  electro- 
lysis as  possible. 


-10- 

PAST  III 
EXPERII.IESTAL 

) 2.  Procedure 

The  tests  were  made  ’oy  the  parallel  analysis  of  five  equal 
portions  of  the  seme  stock  solution,  at  identical  voaLtages  and 
current  strengths,  for  the  same  lengths  of  time.  Five  "runs" 
were  made  on  each  reagent,  and  assuming  the  complete  deposition, 
after  the  proper  tests  v/ere  made,  the  loss  in  weight  of  the  elec- 
trode was  calculated  from  its  last  previous  ?/eight,  alone.  The 
electrodes  save  the  silver  one,  were  cleaned  hy  nitric  acid  of 
a density  pf  1.20g/cc.The  silver  one’  was  cleaned  hy  means  of  con- 
centrated hydrochloric  acid  and  hydrogen  peroxide.  All  drying  of 
electrodes  was  done  at  the  temperature  range  of  100°-106°C  for 
one  half  hour,  this  having  been  found  in  all  cases,  to  "be  suf- 
ficient for  the  present  investigation,  vdth  no  accompanying  danger 
of  oxidation  of  the  metals.  The  time  of  the  electrolysis  was 
without  exception  one  hour  for  the  stationary  work.  In  the  case 
' of  the  cobalt  and  nickel  electrolysBs  there  was  added-  to  the  mixtur 
C.P.  ammonium  sulphate,  to  increase  the  conductivity  of  the  solu- 
tion. 

The  electrodes  used  for  investigation  were  of  gold  gauze, 
pla-tinum  sheet,  platinum  gauze,  "Palau"  sheet,  and  silver  gauze, 
for  the  revolving  anode  worla  For  the  stationary  work  a gold 
dish,  a silver  dish,  and  two  of  platinum  were  used,  each  with  a 
platinum  sheet  anode,  suspended  by  platinum  wire  into  the  elec- 
trolyte. These  are  the  common  metal  electrodes  as  used  in  the 
laboratory  of  the  pivision  of  Analytical  Chemistry  of  the  Uni- 
versity of  Illinois. 


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/ PAHT  IV 

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fa)  With  c/lindrical  stationary  cathode  and  rotary  wire 
srew  anode  the  following  data  were  obtained: 

1.  r^ilver  in  Silver  nitrate 

Cathode  Weight  Before  Electrolysis  Average  loss 

(Metal)  1'  2 3 4 5 Pnring  All. 


Cold  7.6'559 

7,6559 

7.6559 

7.6560 

7.6559 

Silver  10.4245 

10.5432 

10.6620 

10.7808 

10.8993 

* 0.1187  g. 

Palau  10.6234 

10.6233 

10.6232 

10.6231 

10.6230 

--0.0001  g. 

Pt  f gauze  )16 . 7835 

16.7835 

16.7835 

16.7835 

16.7835 

Ptf  sheet ) 9.4013 

''9.4014 

9.4013 

9,4012 

9.4013 

2.  Cobalt 

in  Cobalt  Sulphate 

Cathode  Weight  before  Electrolysis 

Average  Loss 

(Metal)  1 

2 

3 

4 

5 

Luring  All. 

Gold  7.6559 

7.6558 

7.6559 

7.6561 

7.6160 

Silver  10.7664 
Palau  10.6234 

Pt  ( gauze  )1 6.7836 

10.7035 

10.6231 

16,7833 

10.4045 

10.6233 

16.7336 

10.2727 

10.6230 

16.7835 

10.1321 

10.6229 

16.7836 

--0.1561  g.- 

—0,0002  g.- 

Pt( sheet)  9.4014 

9.4013 

9.4014 

9.4013 

9.4013 

3.  Cobalt 

in  Cobalt  nitrate 

Cathode  Weight 

before  Electrolysis 

Average  Loss 

(Metal)  1 

2 

3 

4 

5 

Luring  A.  11 

Gold  7.6559 

7.6559 

7.6559 

7.6555 

7.6557 

--0.0002  g.- 

Silver  10.2263 

10.2747 

9,3217 

8,7941 

8.6480 

—— 0,4067  g.“ 

Palau  10,6234 

10.6231 

10.6233 

10 . 6230 

10.6229 

— — 0,0003  g»— ' 

Pt  (gauze)l6,7835 

16.7835 

16.7835 

16.7835 

16.7836 

Ptfsheet)  9.4013 

9.4013 

9.4013 

9.4012 

9.4014 

4*  nickel  in  nickel  Sulphate 


Cathode  Weight  before  Electrolysis 

(lletal^  12  3 4 

Gold  ' 7,6558  7.6559  7.6559  7.6555 

Silver  10.8993  10.8816  10.8641  10.8460 

Palau  10.6232  10.6233  10,6234  10.6233 

Ptfgauze)16.7835  16.7833  16.7835  16.7833 
Ptfsheet)  9.4012  9.4013  9.4014  9.4014 


Average  Loss 
5 puring  All 
7.6557  --0.00C1  g.-- 
10.8284  --0.0227  g.-- 
10.6229  --0.0001  g.-- 
16.7834  --e.OOOl  g.-- 
9. 4012  


ITT' 


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( 


i 


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-12- 

PAKT  IV 
•EESUTiTS 

(a)  TTith  cylindrioal  stationary  cath.odes  end  rotary  wire 
screw  anodes  the  following  data  were  obtained. 


ilickel  in  Zichel  jiditrate 


Cathode  Weight  before  Electrolysis 
fMetal)  - 1 2 3 4 

Gold  7.6559  7.6558  7.6558  7.6557 

Silver  10.8101  10.8051  10.7999  10.7940 

Palau  10.6324  10.6235  10.6233  10.6235 


Pt f gauze) 10. C835  10.7834  10.7833  1C. 7835 
Pt(gheet)  9.4013  . 9.4013  9.4013  9,4013 


5 

7.6559 

10.7888 

10.6234 

10.7855 

9.4014 


Average  Loss 
Luring  All 


--0.0078  g.-- 
— O.OOOl  g.-“ 


6.  Copper  in  Copper  Sulphate 


Cathode  Weight 
(Metal)  1 
Gold  7.7853 

Silver  10.8307 
Palau  10.6240 
Pt(gauze)16.7835 
Pt ( sheet)  9.4010 


before  Electrolysis 
2 3 4 

7.7850  7.7851  7.6561 

10.8420  10.8209  10.7786 
10.6234  10.6238  10.6233 
16.7835  16.7835  16.7833 
9.4011  9.4011  9.4011 


7.6559 

10.7674 

10.6234 

16.7838 

9.4013 


Average  Loss 
Luring  All 
* special 

--0.0186  g.-- 

--0.0004  g.-- 
— — C.90C1  g.~— 

--0.0001  g.-- 


7.  Copper  in  Copper  ITitra.te 


Cathode  Weight 
h'etal)  1 
Gold  7.6559 

Silver  10.7565 
Peleu  10.6233 
ptfghuze )16.7835 
Pt(gheet)  9.4013 


before  Electrolysis 

2 3 4 

7,6558  7.6559  7.6558 

10.7454  10.7342  10.7220 
10.6232  10.6234  10.6234 
16.7835  16.7835  16.7835 
9.4014  9.4013  9.4012 


5 

7.6559 

10.71C1 

10.6233 

16.5835 

9.4014 


Average  Loss 
Luring  All 


—0.0118  g.-- 


--0.0001  g.-- 


8.  Zinc  in  Zinc  Acetate 


Cathode  Weight  before  Electrolysis 
(Metal)  1 ' 2 3 4 

*Gold  9.9770  9.9770  9.9770  9.9770 

Silver  10.6998  10.6994  10.6956  10.6940 

Palau  10.6233  10.6254  10.6233  10.6234 

*Pt(gauze) 16.9751  16.9750  16.9748  16.9747 
*Pt( sheet)  9.5927  9.5927  9.5927  9.5927 


9.9770 

10.6920 

10.6234 

16.9745 

9.5987 


Average  Loss 
Luring  All 


--0.0019  g.-- 

--0.0001  g.-- 


Plated  witli  copper  to  prevent  the  formation  of  platinum 
black  and  black  gold  which  are  easily  lost  mechanically.  A gold 


-13- 


oomplex  is  formed  whicli  is  soluDle,  if  the  electrode  is  not  pro- 
tected "by  copper. 


The  item  marked  "Average  loss  During  All"  is  the  average 
of  the  four  losses  as  indicated  between  the  five  successive 
weighing’s  in  each  case.  The  item  marked  ’•'special,  for  Gold, 
under  6.  Copperiin  Copper  Sulphate,  is  a corrosion  loss  of  gold 
due  only  to  the  use  of  nitric  acid  of  specific  gravity  1.42,  con- 
centrated to  that  point  by  allowing  it  to  stand  upon  a steam 
bath  over  night,  with  the  electrodes  in  it. 


The  loss  of  weight  of  the  electrode  is  that  occuring 
both  during  the  electrolysis  and  the  succeeding  cleansing;  the 
method  for  cleansing  has  been  previously  mentioned. 


In  the  case  of  the  sine  electrolysis  it  was  advisable, 
inasmuch  as  the \purpose  of  the  study  was  the  chemical  and  elec- 
trolytic action  of  the  reagents,  to  prevent  the  purely  mechani- 
cal losses  due  to  the  formation  of  platinum  black  and  black  gold, 
as  well  as  the  soluble  gold  complex  solution  loss.  Eov/ever  a 
fev/  determinations  were  run  on  some  gold  and  platinum  wire  as 
cathodes,  and  the  results  s-re  of  interest;  they  follow: 


8.  Sine  in  Zinc  Acetate 

Cathode  Weight  before  Electrolysis 

^oldfwire)  0.Q341  0.0237  0.0114 

Plat. (wire)  0.2746  0.2723  0.2710 


Average  Loss 
During  All 
0.0113  g.-  — 

0.0018  g. 


,1  r , 


PART  Y 

Discussion 

There  are  several  points  to  "be  taken  into  consideration 
in  a survey  of  the  results  of  this  work,  including  all  the  physi- 
cal conditions,  as  temperature,  voltage,  amperage,  current  density 
time,  and  the  character  of  the  deposit.  The  latter  tv;o  points 
are  very  closely  related  and  if  all  apparatus  he  strictly  clean 
and  free  from  any  grease,  such  as  "body  oils  from  the  fingers,  it 
is  found  that  the  longer  the  time  of  deposition  the  greater  v;as 
the  density  of  the  deposit,  and  its  adhesion  and  cohesion.  Of 
course  such  a comparison  is  true  as  applied  to  only  one  metal  at 
a time. 

Por  the  purposes  of  discussion  it  seems  well  to  mention 
first  the  simple  electrolytes,  and  later  the  more  complex.  Of  the 
simple  type  the  ones  used  V/cre  silver  nitrate,  copper  sulphate, 
copper  nitrate,  and  zinc  acetate.  The  complex  electrolytes  were 
the  solutions  of  cohalt  and  nickel  salts.  The  word  complex  is 
used  in  this  sense  to  express  the  fact  that  the  metallic  radical 
to  he  deposited  exists  in  the  solution  in  a form  in  which  its 
primary  ionization  is  as  a comlex  ion  which  then  ionizes  to  a 
lesser  extent  into  the  cation  to  he  deposited. 

The  reactions  taking  place  in  the  electrolysis  of  silver 
nitrate,  for  example,  are  primarily  CuflTOg)^— ^ Cu  v SUOg. 

The  copper  ion,  migrating  to  the  cathode,  takes  up  one  electron 
and  is  deposited  as  the  element;  the  ITOg  radical  while  migrating 
toward  the  anode  reacts  with  the  water  to  produce  free  nitric  acid 
with  a liberation  of  molectilsr  hydrogen  at  the  anode.  There  is 


f 


-1£- 


also  liberation  of  hydrogen  from  the  cathode,  though  this  is  not 
8s  marked  as  the  evolution  of  oxygen.  It  is  ^/ell  known  that  this 
' procedure  requires  the  presence  of  a considerable  excess  of  iiitric 
acid  or  the  solutionnwill  become  alkaline  with  an  actual  odor  of 
ammonia  at  the  end  of  the  electrolysis,  in  which  case  the  solution 
resumes  a deep  nlue  color,  and  the  metal  deposited  is  contaminated 
with  oxide.  This  condition  is  brought  aboiit  by  the  action  of 
the  electric  current  on  the  ITHOg  to  produce  nascent  hydfogen  which 
reduces  the  nitric  acid  to  ammonium  nitrate,  perhaps  according  to 
an  equation  resembling  4F-2  ^ HITOg  — sulphate, 
on  the  other  hand,  does  not  suffer  such  reduction,  and  ammonium 
sulphate  will  not  be  present  save  as  traces.  In  the  electrolysis 
of  zinc  acetate  it  is  necessary  to  have  a large  excess  of  acetate 
ion  to  prevent  the  solution  from  becoming  contaminated  by  the  pro- 
ducts of  the  discharge  of  the  acetate  ion. 

In  the  electrolyses  of  the  cobalt  and  nickel  complexes  the 
metals  are  present  in  the  complex  cations,  as  in  (liflTEg^n) , which 
undergoes  a secondary  ionization  and  equilibrium,  as  hi  - 4ITH3 
hiflE3l4  ; cobalt  behaves  in  this  respect  similarly  to  nickel.  To 
prevent  the  formation  of  the  characteristic  nickelous  and  cobaltic 
hydroxides  it  is  necesf^'ary  to  have  present  a high  concentration  of 
OH  ions,  accomplished  by  excess  ammonium  hydroxide.  This  also 
lov/ers  the  concentration  of  the  Co  and  hi  ions  but  prevents  the 
formation  of  the  oxides  and  oxide  hydrates. 

It  seems  from  the  result  obtained  that  the  silver  is  suscep- 
tible to  loss  both  in  the  acid  and  the  alkaline  solutions,  and 
there  i s little  preference  for  either,  thoufch  the  losses  in  the 


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-16- 

zinc  electrolyses  is  markedly  lov/er  than  in  acid  electrolytes. 

This  is  a point  in  favor  of  the  electrodes  of  this  metal,  even 
, ly  the  oeginning  student  in  electroanalysis.  The  average  error 
in  their  use  would  seem  to  he  in  the  neighborhood  of  O.OEOO  grams 
in  each  electrolysis,  and  though  the  acetic  acid  solution  shows 
the  lowest,  w'ith  an  average  loss  of  only  a little  over  C.0019 
grams,  and  the  nitric  acid  next  lowest  with  an  average  loss  of 
a little  over  0.0100  grams  per  run,  the  latter  would  correspond 
to  1^  of  a gram  sample,  and  correspondingly  more  if  the  rating  be 
on  the  percentage  of  the  element  determined.  The  gold  cathode 
lost  slightly  on  first  being  used  in  copper  sulphate,  but  after 
several  cleanings  and  succeeding  use,  assumed  a constant  weight, 
having  apparently  become  passive,  by  the  action  of  the  nitric 
acid  employed  in  the  cleaning.  The  ”Palau’^  electrode  was  some- 
what better  than  the  gold  in  the  matter  of  corrosion,  but  for 
some  reason  the  deposit  on  a cathode  of  this  metal  was  of  a less 
dense  character,  and  times  it  was  quite  difficult  to  get  a good 
adherent  and  coherent  deposit.  Also  this  electrode  tarnished 
easily  and  all  the  colors  of  the  rainbow  would  be  apparent  at  the 
end  of  an  alkaline  electrolysis  on' that  portion  of  the  metal 
which  had  not  been  immersed  in  the  electrolyte.  This  is  the 
reverse  of  v/hat  would  be  exp.ected  for  customisrily  the  lesser 
current  densities  produce  the  denser  deposits,  and  the  ’’Palau" 
electrode,  on  account  of  its  larger  size,  and  consequent  greater 
surface,  had  a.  lower  current  density  in  its  use  than  the  otlers. 

As  would  be  expected,  the  platinum  electrodes,  both  sheet 
and  gauze,  remained  almost  constant  in  weight.  The  only  corrosion 


-17- 

losses  of  the  platimnn,  of  consequence,  occurred  in  the  c!etermina- 
tion  of  zinc,  which  apparently  forms  a surface  alloy,  diffu^jing 
' somewhat  into  the  platinum,  and  yielding  a spongy  deposit  of  plat- 
inum hlack  on  cleaning  the  electrode  with  hydrochloric  acid  or 
sulphuric.  Such  a friable  deposit  is  easily  lost,  and  at  best 
hard  to  7/ash  clean  and  dry  well.  For  this  reason  the  zinc  elec- 
trolyses were  first  rim  on  small,  relatively  useless,  bits  of  v/ire 
of  platinum  and  gold,  as  gold  is  simialrlj^  affected.  Then  the 
electrodes  were  copper  plated  and  in  such  a condition  it  was  found 
satisfactory  to  use  them,  though  there  was  a steady  and  consistant 
loss  of  approximately  0*1  mg  at  each  usage.  This  use  of  copper 
makes  the  zinc  electrolyses  a study  of  the  corrosion  of  copper  on 
those  electrodes  which  v/ere  so  plated,  the  gold  and  platinum,  the 
silver  and  palau,  used  without  this  protecti^on  are  studies  of  the 
effect  on  these  metals  direct.  ' 

In  the  original  plan  of  this  investigation  we  had  the  idea 
of  investigating  tungsten,  molybdenum,  tantalum,  and  "Illium” 
electrodes  as  well  , but  this  had  to  be  abandoned,  due  to  the 
difficulty  of  obtaining  material  suited  to  the  work. 

Stationary  electrodes  ?/ere  found  to  be  very  imsatisfactory 
inasmuch  as  a much  greatef  dilution  was  required,  and  over  eight 
hours  time  in  continuous  electrolysis  was  necessary  to  get  a com- 
plete deposition  of  the  metal.  Within  that  length  of  time  the 
Eouroe  of  current  would  somewhat,  at  times  was  negegible  in 

quantity,  and  there  was  a serious  loss  of  water  by  evaporation  of 
the  electrolytes  during  that  length  of  time,  with  consequent  con- 
j3Laiitratj.cn -xxi*  the.„solutlona*-. — . — . — 


9 


-18- 


In  one  case  when  the  analysis  7/as  left,  at  the  end  of  four  hours 
it  was  in  excellent  progression,  hut  at  the  end  of  the  next  four 
practically  all  the  deposited  copper  had  been  redissolvet"  hy  the 
then  concentrated  nitric  acid  or  remained  high  and  dry  on  the 
sides  of  the  dish,  mixed  with  the  salts  produced  hy  evaporation. 
It  was  found  necessary  for  present  purposes  to  provide  for  the 
replenishiment  of  the  water  of  the  solution. 

Two  analyses  each  were  obtained  for  copper  in  copper  sul- 
phate only,  on  the  three  metals,  gold,  silver,  and  platinum,  out 
of  some  fortliy  trials.  Their  results  are  tshulated  below. 

Other  electrolyses,  of  cobalt,  nickel,  and  zinc,  7/ere  tried  out 
but  proved  unsuccessful. 


Cathode 
f Metal) 
platinum 


5*  Copper  in  Copper  Sulphate 

T7eight  before  electrolysis 


Average  loss 
Piiring  All 


Platinum 


Silver 

Gold 


1 

37.9041 

43*7818 

31.3742 

48.6309 


37.9040 

43.7818 

31.1718 

48.6310 


p 


--0.2024  g.-r 


I 


>1  .•  • 


I 


-19- 
PAF.T  YI 

In  suiaraing  up  the  results  of  this  investigation  it  must 
he  admitted  that  there  is  no  logical  way  of  expressing  the  cor- 
rosion losses  found,  in  terms  of  any  absolute  values  v/hich  might 
lead  to  theoretical  conclusions;  there  is  too  great  a variation 
for  that.  The  only  conclusions  that  are  well  grounded  ere  those 
of  a qualitative  estimation  of  the  usefulness  of  the  metals  for 
cathode  use  in  electros-na lysis. 

It  seems  that  the  use  of  silver  is  out  of  the  question, 
for  its  losses  in  all  kinds  of  solutions  negative  the  advantage 
of  a low  initial  cost.  Gold  appears  suitable  from  the  stand- 
point of  corrosion  alone,  hut  because  of  its  lack  of  rigidity, 
is  easily  spoiled  mechanically,  particularly  by  the  beginner. 

Palau  ware  is  apparently  alright  from  the  corrosion  standpoint, 
and  the  tarnish  it  sometimes  has  is  unweighable,  but  it  has  the 
handicap  of  being  unobtainable  in  the  gauze  form,  and  in  sheet 
form  takes  a deposit  that  is  often  nonadherent.  Platinum 
fulfills  all  the  requirements  of  the  electroanalyst • 

The  author  of  this  thesis  believes  that  the  best  electrode 
is  the  one  in  which  the  surface  exposed  to  deposition  from  the 
electrolyte  is  of  the  same  metal  as  that  deposited,  plated  or  sol- 
id; this  is  of  course  general,  as  it  is  recognized  that  zinc 
may  well  oe  plated  upon  copper,  etc. 

A rigid  gold  gauze  electrode  v/ould  be  the  cheapest  of  the 
effective  electrode  materials  tested. 


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